Zasova L.V., Shakun A.V., Khatuntsev I.V., Ignatiev N.I,(1,2), Brekhovskih U.A.(1), Piccioni G.(3), Drossart P.(4). (1) IKI RAS, Moscow, (2) MIPT, Dolgoprudny, Russia, (3) lAPS-INAF, Rome, Italy, (4) LESIA, Meudon, France O 2 night airglow in Venus atmosphere and dynamics around 100 km from VIRTIS-M VEX MS3,

O 2 Venus night airglow as a tracer of circulation near mesopause O + O + CO 2 --> O 2 * + CO eV - recombination O 2 * --> O 2 + hv - de-excitation O 2 * + M --> O 2 + M - quenching Subsolar-to-antisolar circulation (SS - AS) in thermosphere Retrograde zonal superrotation (RZS) in mesosphere

1,2 (black,red) –limb spectra – only O2 emissions bands. 3-4 (green, blue) – on the disk of the planet, peaks of thermal emission of low atmosphere and surface µm peak is a superposition of the non-LTE O 2 and thermal emissions. Max O µm, max thermal radiation – µm VIRTIS-M is mapping spectrometer with spectral range µm. Spectral resolution in IR of µm at 1.27 µm. Two modes of work – nadir and limb. Data – cubes: two coordinates of point + spectrum Examples of the O 2 vertical profiles H,km Volume emission rate W/m2/m/sr

– MR units conversion coefficient Equation for the O2 intensity calculation: – Lambert cloud albedo (Crisp et al. [1996]) – aspect ratio 1.27 /1.18 of thermal emission of the atmosphere – path in the layer - VIRTIS-M measured spectral intensity Thermal emission Intensity at 1.27 µm

It was chosen 27 areas without visible O 2 emission. They occur in the range of surface altitudes from -2 km to +2.5 km. Measured spectra were corrected for errors, not taken into account in calibration procedure. Spectra for these areas were fitted by modeled ones by variation of clouds opacity and the H 2 O mixing ratio. Surface elevation was taken from Magellan data. Example of fitting spectra.Measured (triangles) and synthetic spectra (solid line), orbit 320

The importance to take into account altimetry Magellan altimetry The O 2 emission distribution with k=const. Artifacts due to surface elevation features are seeing in the O 2 distribution The O 2 emission distribution with k=k(h). Artifacts disappeared.

6MR Orbit 66 (data cubes 00, 01) Maximum emission at AS area Subsolar-antisolar flow Orbit 82 (data cubes 00,01,03) Maximum at 22 h shifted in opposite direction to RZS Orbit , Maximum at 2-3 h in equatorial region RZS with up to 60 m/s Orbit 319 (data cubes 01,02) Maximum emission at 23 h at equator shifted in opposite direction to RZS RZS φ° (X-axis –local time, unique for all plots) MAPS of theO μm night airglow

6MR 321 (00,01) 351 (00 -05) 367 (02) Several maxima h, 4-6 MR RZS up to 60m/s Orbit 380 (01-11) LT = -3 ÷ 3h No symmetry Two maxima: φ = 5°, LT = 0h, 6 MR φ = -30°, LT = 23 h, 4.5 MR RZS Two symmetrical maxima

505 (01-03) 388 (09-14) 390 (04-13) 567(04,06,08,12,14) 569 (04,06,08,10,12,14) 565 (04,06,12,14) RZS

579 (00,04,06,08,10,12) (00-08) 579 (00,04,06,08,10,12,14) 598 (00-06) 597 RZS (02,03)

MAP of the O 2 (a 1 ∆ g ) airglow based on 718 orbits Only measurements with exposure ≥ 3 s were used to avoid noisy data (left). Corresponding number of orbits for averaging at each point (right). I av = 0.35±0.3 MR Intensity, MR Number of orbits Latitude Zonal wind

Mean intensity on the evening side is 0.43 MR Mean intensity on the morning side is 0.26MR Intensity of the O 2 airglow vs. local time for different latitudinal zones, averaged over 10 ° latitude and 2h local RZS

Vertical emission rate, MR Local time, h Limb data. Averaged over 10 deg. of latitude and 2h of local time At latitude 50N maximum of intensity of O2 airglow is before midnight and minimum after midnight. I =0.45±0.36 MR, H peak =97 ± 3km, Half-width= 8 ± 3 km RZS H, km W/m2/m/sr Volume emission rate

Krasnopolsky (2010), photochemical model, based on 64 reactions 4 πI O2 = (Φ O /10 12 ) 1.14 MR Observed O 2 nightside-mean airglow intensity of 0.35 MR requires the O atoms flux of 2.2·10 12 cm -2 s -1 Maximum of 6 MR – 2.4·10 13 cm -2 s -1 According to Krasnopolsky (2010), the dayside-mean production of O by photolysis of CO 2 above 80 km is ·10 12 cm -2 s -1 at low and high solar activity, respectively. It is concluded that the model support the observations of the O µm nightglow with mean intensity less than 1 MR

Thermal tides (Venera-15, Zasova et.al 2007) Amplitudes of diurnal (T1 )and simi- diurnal (T2) exceed 5K between km at low latitudes Gravity waves (Altieri et al. this session)

Pioneer Venus SPICAV/VEX NO – maximum emission around 2h (PV, and PICAV). RZS above 100 km is important, up to 60m/s - Brecht et al. (2011)

Map of the O2 emission intensity(MR) and horizontal wind speed (arrows) –top Horizontal divergence in S -1 – bottom panel

- Circulation at mesopause is combination of SS-AS, zonal superrotation and waves activity, relative importance of all components is time variable -In the map ( averaged over 718 orbits ) emission maximum is observed at low latitudes, around midnight (20 N - 20 S, LT =22 h- 3 h, without absolute maximum in antisolar point ) for both nadir and limb measurements -At individual maps a maximum intensity may be found in the range of local time - 4 h - +4 h. Shift of maximum emission to morning terminator may be connected to superposition of SS-AS and RZS. Opposite shift we don’t understand. Sometimes symmetrical behaviors vs. local time is observed Wave activity also may be responsible for deviation of the O 2 distribution from the case SS-AS. -Low intensity near terminators as well as wide spot of higher intensity around midnight ( on average map ) indicate on wind flows through terminators from the day side. SS-AS is important mode of circulation - Comparison with NO night glow distribution ( with map, obtained by Pioneer-Venus ) show both correlation in some cases and anticorrelation in others. -O 2 and NO emissions are related to different layers in the atmosphere -To explain observed maps of the O 2 emission it needs GCM for mesosphere with included photochemistry SUMMARY

Вертикальное распределение эмиссии O 2 (a 1 ∆ g ): Интенсивность эмиссии: 0.45 ± 0.36 МРл Высота максимума эмиссии: 97 ± 3 км Ширина профиля на половине максимума эмиссии: 8 ± 3 км